Have you ever wondered why you can back squat more than you can front squat?

As pictured above, barbell position determines back angle. In a successful, weighted squat, the barbell will remain over the middle of the foot. If we place the barbell lower on our shoulders (as in the low bar back squat) we allow our torso to cantalever forward, increasing hip flexion (closing), which lengthens and creates tension in the hamstrings. This allows us to drive our hips out of the bottom of the squat, sending the knees back and maintaining the length and tension in the hamstrings as we rise. Because the hamstrings are used to extend (open) the hips as we come out of the squat, more tension in those muscles allows for more power in the lift. If you lead with your chest coming out of the bottom of the squat, you create a more vertical back angle which keeps the knees slightly forward, shortening and reducing the tension in the hamstrings and taking a significant amount of power out of the lift.